It's an extremely complex issue and your question/opinion is in the most simple of terms.
It's easy to say just stop letting them in and round up those here, educate them on the process and send them back.
Are current citizens ready to pay the costs that stopping it will cost?
From stopping entry to increased labor costs in agriculture, construction and many other labor sensitive industries.
Do we uproot families that have been here for 20 yrs and kids that have grown up here?
We must control entry to the US.
We must gradually change industries that rely on cheap labor, that current citizens don't want to do.
We must discourage employers from using illegal workers.
We must find a fair way to deal with those that are here now and were encouraged to come by our own fault.
But make no mistake, our own immigration policy mistakes if the past are going to cost US a fortune to correct.
In both fianclal and moral capital.